The permittivity dependence of the trans to cis isomerization barrier of diphenylbutadiene (DPB) observed previously in n-alcohols is shown to extend to alkyl nitriles and chlorinated solvents. Kramers’ expression predicts the observed DPB isomerization rate constants in these solvents when evaluated by using the barrier height given by the permittivity dependence developed in n-alcohols. In contrast, the observed DPB isomerization rate constants in mixtures of ethanol and hexane were substantially lower than predicted, indicating either differences between the bulk and local composition or differences in the way the mixed solvent orders itself in the vicinity of the solute.